Add support for eager relations

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Is your feature request related to a problem? Please describe.

Now we have no option to describe eager relations. Some way to mark eager relations is necessery for supporting loadEagerRelations typeorm option.

Describe the solution you'd like

By either adding new EagerRelation type annotation or adding an option to existing Relation type.

Describe alternatives you've considered

Additional context

Add any other context or screenshots about the feature request here.